1. Field of the Invention
This invention concerns selectively deslagging partial oxidation reactors.
2. Description of Related Information
Petroleum, coal and other organic natural resources are used to make fuels, such as for transportation, heating and power generation, as well as feedstocks to make materials which go into most manufactured goods, including clothes, food, cars, buildings and other merchandise. Diminishing resources have led to increasing use of organic feedstocks generally, and particularly in the United States, which are of lower grade and from more impure sources, such as heavier and poorer quality crude oil. These impure feedstocks need to be refined, or upgraded, more than lighter petroleum to make products having acceptable properties. A common upgrading process, called coking, recovers valuable hydrocarbon products from residual oils or other low grade petroleum products. Coking produces carbonaceous by-products called coke. Coke, residual oils and by-products made from heavy crude oil are generally impure containing relatively high levels of contaminants such as sulfur and various metals like vanadium, nickel and iron.
Unlike high purity grade coke which can be used to make electrodes, impure coke has little value due to the contaminants. Impure coke, as well as other carbonaceous materials containing metal contaminants can, however, be used as feedstock for partial oxidation reactions producing mixtures of hydrogen and carbon monoxide gases, called synthesis gas, or simply syngas. Syngas is a feedstock for making a host of useful organic compounds or can be used as a clean fuel to produce power in an environmentally sound way.
Partial oxidation of impure coke or other contaminated materials produces slag by-product which collects on the inside surface of the partial oxidation reactor. The slag deposits build up in the reactor or outlet to a level which prevents effective partial oxidation requiring shutdown to remove slag, called deslagging, from the partial oxidation reactor.
Slag deposition can be avoided by adding materials which prevent solid slag deposition, such as fluxing agents, which prevent slag solidification, or washing agents, which help carry slag from the reactor. These additives prevent slag build-up generally by mixing with the metal contaminants to prevent slag formation or its ability to build up deposits in the reactor. The use of these additives can be disadvantageous by increasing the amount of solid by-product of the partial oxidation reaction and by lowering by-product recovery value by diluting the concentration of valuable slag components, such as vanadium. The additives can also adversely impact the partial oxidation reaction, such as by reducing reaction efficiency. The use of such additives is described, for example, in U.S. Pat. No. 4,952,380 (Najjar et al.) and the patents therein listed.
Deslagging is limited by the nature of the slag and other components or aspects of the partial oxidation reactor. Due to the high melting point of the solid slag, it cannot be removed simply by heating it until it melts since reactor materials generally cannot withstand such high temperatures. Slag which can be derivatized to another form having a lower melting or subliming point provides an opportunity for slag removal. However, merely derivatizing the slag and heating the reactor to make fluid, derivatized slag will generally produce derivatized slag which solidifies in and blocks the reactor outlet, thereby requiring slag removal by mechanical means. Alternatively, U.S. Pat. No. 4,525,176 (Koog et al.) describes a deslagging technique using a movable burner assembly to control slag removal and avoid blocking the reactor outlet.
Deslagging can also damage the reactor. Refractory used to insulate the reactor vessel can be corroded, eroded or otherwise attacked by molten slag, and particularly derivatized slag such as pentavalent vanadates. Damaged or lost refractory needs to be replaced and requires reactor shutdown.